This grant application represents the request for continuing support for the study of the renin-angiotensin-aldosterone system and its role in regulating renal electrolyte excretion and controlling blood pressure. For the upcoming year the research will focus on the significance of the recently demonstrated association between urinary potassium excretion and plasma aldosterone in a large number of subjects (recently reported from this laboratory). In addition, a negative correlation between potassium and diastolic blood pressure was identified suggesting that patients with elevated blood pressure had in general a lower potassium intake than did normotensive subjects. Since this observation raises the question whether a deficit in the potassium intake may play some etiologic role in the pathogenesis of hypertension, the studies for the present year propose to look in more detail at this relationship and whether variations in potassium intake do in fact influence the levels of blood pressure. It is also proposed that the relationship which we have demonstrated between the levels of plasma renin substrate and diastolic blood pressure be explored further by examining the half-life or turnover rate of plasma renin substrate in individuals with different blood pressures ranging from those individuals in the low ranges of normal to individuals with markedly elevated blood pressure. As a butt of the research effort for the coming year, we also propose to attempt to characterize changes in the diurnal pattern of renin and aldosterone plasma levels in response to fluctuations in the electrolyte intake.